Objectives: Persistent low-grade inflammation is related to the development of many chronic diseases. The dietary inflammatory index (DII®) is designed to assess the potential effects of diet on an individual's inflammation status. The aim of this study was to evaluate the construct validity of the DII using inflammation biomarkers in Japanese adults.

Methods: Overall, 565 participants from the food frequency questionnaire (FFQ) validation study of the Japan Public Health Center-Based Prospective Cohort were included in the present study. This cohort consisted of two independently recruited and examined, cohorts I and II. Dietary records (DR) were collected for 28 d and two FFQs were administered. Blood samples also were obtained for the analysis of high-sensitivity C-reactive protein (hs-CRP) and interleukin (IL)-6 concentrations. DII scores were calculated from DR and FFQ using energy-adjusted dietary intakes by the density method. Higher DII scores indicate a greater proinflammatory potential of the diet. The associations between DII and inflammatory biomarkers were assessed using regression models adjusted for age, body mass index, smoking status, and amount of physical activity.

Results: The associations between DR- and FFQ-derived DII scores were moderate. Higher DR-derived DII scores, representing a more proinflammatory diet, were significantly correlated with IL-6, but not hs-CRP, concentrations in men. The geometric means of IL-6 concentrations in the lowest and highest DII quartiles were 1.05 and 1.33 pg/mL (P = 0.02 for trend) in cohort I, and 1.00 and 1.24 pg/mL (P = 0.03 for trend) in cohort II, respectively. Furthermore, IL-6 concentration appeared to increase across DII quartiles calculated from FFQ in men. However, there was no association between DII and inflammatory biomarkers in women.

Conclusions: Null findings in women may reflect the generally lower levels of chronic systemic inflammation among Japanese versus their Western counterparts. These findings indicate that DII may be applied to measure the potential effects of diet on chronic diseases through inflammatory pathways in Japanese men.